Voice warning system

ABSTRACT

A method and digital solid state electronic voice warning system utilizing permanent read only memories. The analog voice signal is limited in both amplitude and frequency prior to conversion to digital form to reduce distortion when the voice message is reproduced.

United States Patent 1191 Panicello et a].

[ Apr. 30, 1974 [5 VOICEWARNING SYSTEM 3,376,387 Cassel 179/1 SA 3,074,065 l/ 1963 [75] Inventors: Joseph F. Pameello, Sepulveda; 2,934,752 4/1960 Michael m Thousand 2,804,501 8/1957 Hart 340/27 R Oaks, both of Calif. O P UCATIO IHER UB NS [73] Assignee: LockheedAircraft Corporation,

Burbank, Calif H. Nussbaumer and Picard, Audlo Response Unit, IBM Technical Dlsclosure Bulletin, Vol. ID No. Filed: 11, 1971 7, December 1967, pages 938 and 939 21 Appl. No; 170,779

- Primary Examiner-Kathleen H. Claffy Assistant Examiner-Randall P. Myers [52] US. Cl 340/27 R, 340/148, 340/181 Anomey Agent, or Firm Ge0rge C Sullivan; Ralph 51] Int. Cl G08g 5/00 M mygaw Frank L Zugelter [58] Field of Search 340/27 R, 27 SS, 27 NA,

IMO/181,148, 152 R, 173 R, 174 SP, 147 LP, 413, 173, 173 AN; 179/1 SA, 5 R, 5 P [57] ABSTRACT I v A method and digital solid state electronic voice warn- [56] References cued ing system utilizing permanent read only memories. UN STATES PATENTS The analog voice signal is limited in both amplitude 3,641,496 2/1972 Slavin 340/148 and frequency prior to conversion to digital form to 3,634,625 1/1972 Geohegan, Jr. et a1. 179/1 SA reduce distortion when the voice message is repro- 3,588,353 6/1971 Martin... 179/1 SA d d 3,582,949 6/197] Forst 340/27 R 3,581,014 8/1971 Vogel et al. 340/181 12 Claim, 5 Drawing Figures 38 35 BIASING (c) sauna (E) 8 8 58 LIMIT MOLD 54 8 (D) COMPARATOR .9- RAMP (F) 56 \(G) GEN. 34 N746 BUFFER t (m 5 I I R o so so I 2 CLOCK 1'1 3, I 4o 44 i BAND-PASS 2 52 D9 FILTER N32 68 30 J 64 2 7o 72 74 a w MMV CONVERTER O/A e e s 2 BINARY STORAGE PATENTED m 30 (9M SHEET 1 OF 4 ADDRESS LOGIC MESSAGE STORE CONVERTER SPEAKER SENSOR SENSOR SENSOR JOSEPH F. PANICELLO w N R A O M T D EE I V R N Fl 8 L F- A H m M PATENTEDAPR 30 I914 3.808.591

SHEET 3 OF 4 4 (n l I l (mam 1 (E) l 1 J1 l -m- PM ll l w JOSEPH F. PANICELLO hme MICHAEL s. FRIEDMAN k INVENTORS.

. 1 VOICE WARNING SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a digital voice warning system, and more particularly to the method and apparatus for producing a nondestructive, digital memory of a voice warning message for subsequent nondestructive readout.

Voice warning systems are today used as an adjunct to or a replacement for the warning lights, buzzers, and other indicators in many prior art emergency or alarm condition applications. By the use of voice warnings, the attention of the person responsible for corrective action is immediately directed to the malfunction or adverse condition, irrespective of the direction of his gaze and his preoccupation with other matters at the moment the malfunction or alarm condition occurs. Such systems are of particular advantage in an aircraft where it is desired that the attention of the pilot be gen-- erally directed outside of the-cockpit of the aircraft and where the conditions to be monitored are great in number. Sensors may, for example, be located in appropriate positions about the aircraft to indicate the position of the landing gear, the fuel supply, engine fires, and other malfunctions and/or potential emergency conditions of the aircraft. The use of a voice warning system by which the pilot's attention is specifically directed to the appropriate corrective action bythe content of the voice message may eliminate confusion between one hundred or more visual indicators and the time for pilot response to the alarm condition greatly reduced.

Prior voice warning systems have included messages or portions thereof prerecorded on magnetic tapes or wires for playback 'in response to an alarm condition. Magnetic recordings are, however, particularlysusceptible to the magnetic fields associated with the abrupt energization and'deenergization of high voltage equipment aboard the aircraft as well as other stray magnetic fields. These and other types of recordings may suffer from' similar disadvantages and, in addition, may be adversely affected by the buffeting of the aircraft as a result of turbulence encountered during flight, and particularly by the shocks of repeated landings. Extensive effort is generally made to effect magnetic shielding of the equipment and'to provide the desired shock absorbing mountings for the equipment- It is accordingly an object of the present invention to obviate the deficiencies of known systems of this type and to provide a novel method and voice warning system.

It is another object of the present invention to provide a novel method and voice warning system substantially immune to magnetic fields and shocks.

It is still another object of the present invention to provide a novel method and voice warning system utilizing digital permanent read only memories.

It is yet another object of the present invention to provide a novel method and solid state electronic voice warning system in which the necessity for moving parts has been eliminated.

It is yet still another object of the present invention to provide a novel method and voice warning system in which the voice messages are repeated at intervals until the system is disabled.

These and other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from the claims and from a perusal of the following detailed description when read in conjunction with the drawings.

THE DRAWINGS FIG. 1 is a functional block diagram of the present invention as installed on an aircraft;

FIG. 2 is a functional block diagram of the apparatus for creating. the digital read only memories utilized in the system of FIG. 1;

FIG. 3 is a tinting diagram illustrating waveforms at various points in the system of FIG. 2;

FIG. 4 is a more detailed functional block diagram of the system of FIG. 1;.and

FIG. 5 is a functional block diagram of the digital-toanalog converter of FIGS. 1, 2, and 4.

THE DETAILED DESCRIPTION An understanding of the present invention may best be gained from a perusal of the following detailed description of a preferred embodiment.

The Overall System The present invention is hereinafter described in the embodiment of a cockpit or pilot warning system for use in an aircraft. As illustrated in FIG. 1, a plurality of sensors 10- 14 may be provided at selected positions on the aircraft. For example, the sensor 10 may be adapted to sense the down and locked position of the landing gear, and sensor 12 may be adapted to sense a low fuel supply.

The output signals from the sensors 10 14 are applied to the address logic circuit 16 of the digital message store 18. When properly addressed, the store 18 provides the appropriate digital output signal. This digital signal is converted to analog form in a digital-toanalog converter 20, amplified by a conventional amplifier 21 and transduced by a cockpit speaker 22 (or headset) into a" voice warning signal for the pilot.

The method and apparatus by which the digital message store is created and the method and apparatus by which the stored digital message is converted to analog form and transduced into sound are hereinafter described in greater detail in connection with FIGS. 2

The Encoder With reference to FIG. 2, a conventional microphone 30 is utilized to convert compressional wave energy (sound) into an electrical signal having a frequency range from about 20 Hz. to about 20 KHz. This electrical signal is applied to a conventional bandpass filter 32 which reduces or limits the frequency range of the electrical signal from about 200 Hz. to about 3 KHz. The filtered output signal from the bandpass-filter 32 is applied through a conventional buffer amplifier 34 to a conventional biasing and limit circuit 36.

The biasing and limit circuit 36 limits the amplitude of the electrical signal applied thereto to a predetermined value, and also biases or offsets the electrical signal output therefrom so that the most negative peak of the signal has a zero or slightly positive amplitude to insure a unipolar outputsignal. The output signal from the biasing and limit circuit 36 is applied to a conventional sample and hold circuit 38 which periodically samples the amplitude of the input signal and which holds the sampled value for a predetermined period of time.

The sample and hold circuit 38 is controlled by clock pulses from an output terminal 40 of a conventional clock circuit 42. The clock circuit 42 has a second output terminal 44 and provides a second periodic clock signal at a frequency differing from the frequency of the sample clock signal on the terminal 40.

The frequency of the first or sample clock signal is desirably greater than twice the highest frequency passed by the filter 32 sothat the reproduction of the sampled signal is complete and unambiguous. If the sampling rate is too low, i.e., less than twice the highest frequency sampled, significant information may be lost and distortion introduced.

The frequency of the second clock signal is desirably a multiple of the frequency of the first clock signal and should be sufficient to provide adequate amplitude discrimination of the sampled signal as will hereinafter be apparent.

The clock signal applied to the sample and hold circuit 38 is also applied to a conventional ramp signal generator 46 and to the set input terminal S of a conventional binary element or flip-flop 48. The second clock signal is applied to one input terminal 50 of a conventional two input terminal AND gate 52. The output signals from the sample and hold circuit 38 and the ramp signal generator 46 are applied, respectively, to the two input terminals 54 and 56 of a conventional comparator circuit 58. The output signal from the comparator circuit 58 is applied to the reset input terminal R of the flip-flop 48 and the output signal from the true or binary ONE output terminal of the flip-flop 48 is applied to the other input terminal 60 of the AND gate 52.

The output signal from the AND gate 52 is applied to a converter 62 which may, for example, comprise a plurality of serially connected conventional binary elements or flip-flops with the signals present on the true output terminals thereof gated in parallel to the digitalto-analog converter 68 by the leading edge of the pulses in the sample clock signal. This gate pulse may, for example, be taken from the pulse or binary ZERO output terminal of a conventional monostable or oneshot multivibrator 69 and may also be utilized to reset the flip-flops of the converter 62.

The output signals from the collective output terminal 64 thereof are applied to a conventional and suitable binary storage circuit 66 and to a digitaI-to-analog converter 68, hereinafter described more fully in connection with FIG. 3. The analog output signal from the converter 68 is applied by way of an output terminal 70 through a suitable conventional amplifier 72 to a conventional speaker 74 having the desired audio frequency fidelity.

Encoder Operation The operation of the encoder described supra may best be understood with reference to the waveforms illustrated in FIG. 3.

With continued reference to FIG. 2, and with reference to the waveforms of FIG. 3, the microphone converts in a conventional manner a desired voice message into an analog electrical signal representative thereof. A portion of such an analog electrical signal is illustrated as-waveform (A) in FIG. 3. The frequency range of the analog electrical signal from the microphone 30 is limited in the bandpass filter 32 to reduce the harmonic distortion of the subsequently synthesized signal, i.e., the output signal from the digital-toanalog converter 70.

After amplification in the buffer amplifier 34, the amplitude of the analog signal is compressed, as illustrated by waveform (B) of FIG. 3, and the amplitude of the analog signal is positively biased to insure a unipolar output signal (waveform C). This is accomplished in the biasing and limit circuit 36 by the addition of a dc. bias equal to the amplitude limit of the waveform (B). The non-linear amplitude compression does not affect normal signals, but compression at higher amplitudes will maintain the analog signal within the conver sion range of the encoder so that popping noises in the synthesized signal are reduced.

The leading edge of each pulse in the first or sample clock signal illustrated as waveform (D) in FIG. 3 sets the flip-flop 48 to apply a high level binary signal in the input terminal 60 of the AND gate 52. In addition, each clock pulse causes the sample and hold circuit 38 to sample the amplitude of the analog signal (waveform C) to produce the signal illustrated as waveform (E) in FIG. 3. The trailing edge of each of the clock pulses in waveform (D) resets the sample and hold circuit 38 and maintains the reset condition until the leading edge of the next clock pulse, as is shown in waveform (E). Thus, the comparator circuit 58 is inoperative in the absence of a clock pulse.

The leading edge of the clock pulse in waveform (D) also enables the ramp generator 46 to initiate the generation of a ramp signal, such as that illustrated in a dashed line as waveform (E) in FIG. 3. The ramp signal (waveform F) is desirably linear and reaches maximum amplitude on the trailing edge of the clock pulse to reset the ramp generator 46 until the generation of the next clock pulse.

The ramp signal (waveform F) is applied to the comparator 58 together with the sampled value (waveform E) of the amplitude limited and biased voice signal. When the two signals become equal in value, the comparator circuit 58 generates an output pulse as is illustrated in waveform (G) of FIG. 3. The pulses in waveform (G) are utilized to reset the flip-flop 48, thereby removing the enabling signal (waveform H) from the input terminal 60 of the AND gate 52 until the flip-flop 48 is again set by the leading edge of the next clock pulse in the sample clock signal (waveform D).

Pulses from the second clock signal (waveform I) are passed through the AND gate 52 to the converter 62 for the duration (t) of the output signal from the flipflop 48 (waveform l-I), i.e., from the leading edge of a clock pulse in the sample clock signal (waveform D) to the generation of the reset pulse (waveform G) by the comparator 58. The number of pulses in the second clock signal passed through the AND gate 52 to the converter 62 is thus representative of the sampled amplitude (see waveform J).

The converter 62 is conventional in operation and temporarily stores the count representative of each sample until the count associated with the next sample is available. During this time interval, the converter 62 is operative to convert the count, for example, as shown in the collective waveform (K) of FIG. 3, wherein pulses are gated by the trailing edge of the clock pulse (waveform D) on parallel lines in accordance with the state of the flip-flops in which the binary count is stored. The binary output signal from the converter 62 may be applied to the storage device 66 and may also be applied to the digital-to-analog converter 68 which decodes and reconverts the signal to analog form for amplification in the amplifier 72 and conversion to sound in the speaker 74. By using the digital-toanalog converter 68, the amplifier 72, and the speaker 74, the digital representation of the message may be monitored for clarity and distortion as it is being stored in the storage device 66.

Storage The storage device 66 of FIG. 2 may be any suitable conventional apparatus. The ultimate message store 18 of FIG. 1 is preferably solid state and must be permanent despite power recycles, stray magnetic fields, etc.

The storage device of the present invention is preferably a'metal oxide semiconductor (MOS) or bipolar read-only memory (ROM) in which the data is permanently stored during manufacture. The ROM may be either static or dynamic, depending on the desired clocking function and power dissipation, and may be fabricated by conventional techniques.

Playback The message in the read only memories of the present invention may be addressed by any suitable conventional logic circuit to provide a binary coded signal of the type illustrated in waveform (K) in FIG. 3. This digital message signal is applied, as is illustrated in FIG. 1, to the digital-to-analog converter 20 for conversion to analog form.

With reference now to FIG. 4, the sensors of FIG. 1 may be electrically connected to the set input terminal S of a conventional binary element or flip-flop 76. The output signal taken from the true or binary ONE output terminal of the flip-flop 76 is applied to one input terminal 78 of a three input terminal AND gate 80. The output signal from the AND gate 80 is utilized to trigger a line counter 82 in a message circuit 83. The line counter 82 may comprise, for example, a series of serially connected binary flip-flops.

During the period of time when the AND gate 30 is enabled by the flip'flop 76, pulses from a conventional pulse generator or clock 85 are passed by way of an input terminal 87 of the AND gate 80 to the input terminal of the line counter 82.

The line address pulses taken, for example, from the true output terminal of each of the flip-flops in the counter 82 are applied to a conventional decoder 84 where the binary number from the counter 82 is converted to an enabling signal for successive lines of the ROM matrix 88. This ROM matrix 88 is thus addressed in a conventional manner to effect the non-destructive sequential reading of the lines thereof.

The line counter 82 also supplies an input signal to a row counter 86 which may conveniently be identical to the line counter 82 to provide a series of binary numbers to a decoder 90. The decoder 90 may conveniently be identical to the decoder 84, and sequentially enables the rows of the ROM matrix 88. Either or both of the decoders 84 and 90 may be physically built into the ROM matrix 88, if desired.

All of the lines of the ROM matrix 88 are thus S6- quentially enabled for each of the rows thereof. Upon the enabling of the last row of the ROM matrix 88, a pulse is applied to the trigger input terminal of a conventional monostable or one-shot multivibrator 92 which supplies a negative output pulse from the false output terminal thereof to an input terminal 94 of the AND gate 80. The negative pulse from the multivibrator 92 inhibits the AND gate for the duration of the pulse, i.e., a predetermined period of time selected to permit the pilot to note the message and to reset the system by a manually operated switch 96 in the line between a source of positive potential and the reset input terminal R of the flip-flop 76. Resetting the flip-flop 76 removes the enabling signal from the terminal 78 of the AND gate 80, thus inhibiting the application of clock pulses to the line counter 82. The manual switch 96 may also be utilized to effect lockout of the sensor 10 signal for a predetermined period of time, if desired. Without this lockout of the sensor 10, the condition sensed, if persisting, will again set the flip-flop 76 to renew the voice warning.

The negative pulse from the multivibrator 92 may conveniently be utilized to reset in a conventional mannerthe counters 82 and 86 so that the indexing of the ROM matrix 88 will begin with the appropriate message bit.

The output signals from the ROM matrix may be applied in parallel to an input terminal 104 of the digitalto-analog converter 20 of FIGS. 1 and 2, as hereinafter described in greater detail in connection with FIG. 5.

Each of the other sensors in the system, e. g., the illustrated sensor 12, may be connected to set an associated flip-flop 97 to enable an associated AND gate 98 in the absence of an inhibiting signal from the multivibrator 92. The clock pulses from the clock are passed through message circuit 100 where a ROM matrix is addressed to provide a digital output signal representative of the appropriate message for the condition to which the associated sensor 12 is responsive.

The digital signal from the ROM matrix 88 is, as was explained in connection with FIGS. 1 and 2, converted to analog form in the digital-to-analog converter 20, amplified by the amplifier 21, and transduced to sound by the speaker 22.

With reference now to FIG. 5, where the digital-toanalog converter 20 of FIGS. 1 and 4 is illustrated in greater detail, the digital-to-analog converter 20 receives in parallel the binary output signals from the appropriate ROM matrix as illustrated collectively as waveform (K) in FIG. 3. The pulses which comprise this digital signal are applied in parallel from the collective input terminal 104 to a summing terminal 106 through resistors 108-114. The terminal 106 is a current summation junction and the pulses applied to the resistors 108-1 14 are of the same amplitude. However, the values of the resistors 108-114 are selected so that the current flowing through such resistor will be representative of the decimal number represented by a pulse in that position in the input waveform (K).

By way of example, with the four resistor circuit illustrated in FIG. 5, the resistor 108 will have the value 8R, the resistor 1 10 will have the value 4R, the resistor 1 12 will have the value 2R, and the resistor 114 will have the value R. The current through the resistors 108-1 14 is, of course, inversely related to the value of the resistor so that the increment of current applied to the terminal 106 from a pulse applied through the resistor l 14 will be eight times greater than the increment of current added to the terminal 106 by a pulse applied through the resistor 108.

The terminal 106 is connected to the input terminal 116 of a conventional operational amplifier 118. The output terminal 120 of the operational amplifier 118 is connected to the input terminal 116 thereof by way of the parallel combination of a resistor 122 and a capacitor 124. The addition of the resistor 122 and capacitor 124 feedback loop to the amplifier 118 serves to integrate the signal applied to the input terminal 116. The output signal of the amplifier 118 is applied through a conventional lowpass filter 126 which substantially removes frequency components of the signal above about 3 KHZ for distortion reduction purposes. The output signal from the lowpass filter 126 may be amplified, as shown in FIGS. 1 and 4, by the amplifier 21 and applied to the speaker 22 to be transduced into the voice warning for the pilot.

ADVANTAGES AND SCOPE OF THE INVENTION By means of the present invention, a voice warning system can be implemented in which the stored messages are digital in character and are not subject to inadvertent modification in the proximity of rapidly fluctuating voltages and stray magnetic fields. Moreover, the stored messages are virtually impervious to the shocks normally associated with aircraft landings.

Simplicity and reliability are obtained by the use of digital circuits, and distortion is materially reduced'by the limiting of the analog voice signal in frequency and amplitude prior to the conversion thereof to digital form. This conversion and storage of the digital voice signal may be made in a hospitable environment remote from the environment in which ultimately utilized.

The present invention may thus be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

What is claimed is:

l. A method for generating an audible warning of an equipment malfunction comprising the steps of:

a. generating a continuously variable analog electrical signal representative of compressional wave energy within a frequency range from about Hz. to about 20 KHz;

b. converting the generated analog signal to a corresponding unipolar output signal;

c. periodically sampling the amplitude of frequency components of said unipolar output signal at a fixed sampling rate within a frequency range substantially less than the frequency range of the generated' signal;

d. converting each of the amplitude samples to a corresponding fixed-bit pulse code modulation signal whereby said analog electrical signal is converted to a serial train of fixed-bit-length digital codes;

e. serially storing said fixed-bit digital codes in a nong. generating a train of sequential memory addressing pulses in response to said enabling signal;

h. reading out the content of said memory in a nonrepetitive serial sequence to produce therefrom a sequential series of digital data signals in response to a single application of said memory addressing pulse train thereto;

. converting each of the digital data signals to a corresponding amplitude sample;

j. integrating the amplitude samples to provide an analog signal; and,

k. transducing the analog signal into an audible warn- 2. The method of claim 1 including the step of:

limiting the amplitude of the generated variable analog signal to a predetermined value prior to the unipolar conversion thereof.

3. The method of claim 1 wherein the frequency at which the amplitude of the unipolar output signal is sampled is not less than about 6 KHZ.

4. A method for generating an audible warning of an equipment malfunction comprising the steps of:

a. generating a continuously variable analog electrical signal within a frequency range from about 20 Hz. to about 20 KHz.; I

b. filtering the generated electrical signal to substantially eliminate frequency components below about 200 Hz. and above about 3 KHz.;

c. limiting the amplitude of the filtered signal to a predetennined value;

d. periodically sampling the amplitude of the amplitude limited signal at a fixed sampling rate;

e. converting each of the amplitude samples to a corresponding signal whereby said analog electrical signal is converted to a serial train of fixed-bitlength digital condes;

f. serially storing said fixed-bit-length digital codes in a non-volatile memory circuit;

g. generating an electrical enabling signal in response to an equipment malfunction;

h. generating a train of sequential memory addressing pulses in response to said enabling signal;

i. reading out the stored content of said memory circuit in a non-repetitive serial sequence to produce therefrom a sequential series of digital data signals in response to the application of said memory addressing pulse train thereto;

j. converting each of the digital data signals to a corresponding amplitude sample;

k. integrating the amplitude samples to provide an analog signal; and,

l. transducing the analog signal into an audible warn- 5. The method of claim 4 including the steps of:

converting the amplitude limited signal to a unipolar output signal prior 'to sampling the amplitude thereof.

6. The method of claim 4 wherein the frequency at which the amplitude of the amplitude-limited signal is sampled is not less than about 6 KHz.

7. An aircraft voice warning system comprising:

a plurality of sensors each adapted to sense a condition of the aircraft;

means for storing a digital data signal representative of an audio message for each of said plurality of sensors;

a source of digital pulses having a predetermined pulse repetition rate;

a first binary counter for converting the number of pulses applied thereto to a binary output signal; means responsive to one of said sensors for passing pulses from said source to said first binary counter;

a first decoder for converting the binary output signals from said first binary counter to a line read-out signal;

a second counter responsive to pulses from said first binary counter for converting the number of pulses applied thereto to a binary output signal;

a second decoder for converting the binary output signals from said second counter to a row read-out signal;

a permanent solid-state read-only memory circuit for providing digital data signals in response to said line and row read-out signals, said digital data signals each being relating to the instantaneous amplitude of an audio frequency signal;

second converting means for converting said digital data signals to amplitude samples;

means for integrating said amplitude samples to provide an analog signal; and

means for transducing said analog signal into a voice warning.

8. The system of claim 7 including means for generating a signal for disabling said first converting means; and

means for recycling said first converting means after a predetennined time delay in the absence of a signal from said disabling means.

9. Apparatus for permanently storing signals representative of compressional wave energy comprising:

means for generating an analog electrical signal representative of compressional wave energy within a frequency range from about Hz. to about 20.

KHz.;

biasing means for changing the generated analog signal to a unipolar output signal;

means limiting the amplitude of the generated analog signal to a predetermined value prior to the changing of said analog signal to a unipolar output signal;

means for periodically sampling the amplitude of frequency components of said unipolar output signal within a frequency range substantially less than the frequency range of the generated signal;

converting means synchronized with said sampling means for generating a series of pulses related in number to the sampled amplitude, and for convertan equipment malfunction, comprising:

a source of continuously variable analog electrical signals representative of an audio message;

,means for biasing said analog signals to result in a corresponding unipolar output signal;

means for periodically sampling the instantaneous amplitude of said unipolar output signal at a fixed sampling rate within a frequency range substantially less than the frequency range of said analog signal;

a non-volatile digital memory for serially storing a plurality of fixed-bit length digital codes;

means connected to the output of said sampling means and to the input of said digital memory for converting each of the amplitude samples from said sampling means to a corresponding fixed-bit pulse code modulation signal for storage in said memory as serially-arranged fixed-bit-length digital codes;

means for producing an electrical enabling signal in response to an equipment malfunction;

means for generating a train of sequential memory addressing pulses in response to said enabling signal;

means connecting said memory addressing pulse generating means to said digital memory whereby the content of said digital memory is read out in a nonrepetitive serial sequence to produce, at the output of said memory, a sequential series of digital data signals in response to each application of said memory addressing pulse train thereto;

means for converting each of the digital data signals from the output of said memory to a corresponding amplitude sample;

means for integrating the amplitude samples from said digital signal converting means to provide an analog output signal; and

means for transducing said analog output signal into an audible warning.

11. Apparatus for generating an audible warning of an equipment malfunction, comprising:

means for generating a continuously variable analog electrical signal within a frequency range from about 20 Hz. to about 20 KHz.;

means for filtering said analog electrical signal to substantially eliminate frequency components therefrom below about 200 Hz. and above about 3 KHz;

a limiter for constraining the amplitude of the filtered signal to a predetermined value;

sampling means for periodically sampling the amplitude of the amplitude-limited signal at a fixed sampling rate;

means connected to the output of said samplin means for converting each of the amplitude samples to a corresponding signal whereby said analog electrical signal is converted to a serial train of fixed-bit-length digital codes at the output thereof;

a non-volatile digital memory connected to the output of said converting means for serially storing said train of fixed-bit-length digital codes;

means for producing an electrical enabling signal in response to an equipment malfunction;

means for generating a train of sequential memory addressing pulses in response to said enabling signal;

means connecting said memory addressing pulse generating means to said digital memory whereby the content of said digital memory is read out in a nonrepetitive serial sequence to produce, at the output of said memory, a sequential series of digital data signals in response to each application of said memory addressing pulse train thereto;

means for converting each of the digital data signals from the output of said memory to a corresponding amplitude sample;

means for integrating the amplitude samples from said digital signal converting means to provide an analog output signal; and

means for transducing said analog output signal into an audible warning.

12. Apparatus for permanently storing signals representative of compressional wave energy comprising:

means for generating an analog electrical signal representative of compressional wave energy within a frequency range from about 20 Hz. to about 20 KHz.;

biasing means for changing the generated analog signal to a unipolar output signal;

means for limiting the amplitude of the generated analog signal to a predetermined value prior to the changing of said analog signal to a unipolar output signal;

means for periodically sampling the amplitude of frequency components of said unipolar output signal within a frequency range substantially less than the frequency range of the generate signal;

converting means synchronized with said sampling means generating a series of pulses related in number to the sampled amplitude, and for converting the number of generated pulses into binary form; and,

a solid-state non-destructive read-only memory for permanently storing the digital signals.

l l IF I l 

1. A method for generating an audible warning of an equipment malfunction comprising the steps of: a. generating a continuously variable analog electrical signal representative of compressional wave energy within a frequency range from about 20 Hz. to about 20 KHz; b. converting the generated analog signal to a corresponding unipolar output signal; c. periodically sampling the amplitude of frequenCy components of said unipolar output signal at a fixed sampling rate within a frequency range substantially less than the frequency range of the generated signal; d. converting each of the amplitude samples to a corresponding fixed-bit pulse code modulation signal whereby said analog electrical signal is converted to a serial train of fixed-bitlength digital codes; e. serially storing said fixed-bit digital codes in a nonvolatile digital memory; f. generating an electrical enabling signal in response to an equipment malfunction; g. generating a train of sequential memory addressing pulses in response to said enabling signal; h. reading out the content of said memory in a non-repetitive serial sequence to produce therefrom a sequential series of digital data signals in response to a single application of said memory addressing pulse train thereto; i. converting each of the digital data signals to a corresponding amplitude sample; j. integrating the amplitude samples to provide an analog signal; and, k. transducing the analog signal into an audible warning.
 2. The method of claim 1 including the step of: limiting the amplitude of the generated variable analog signal to a predetermined value prior to the unipolar conversion thereof.
 3. The method of claim 1 wherein the frequency at which the amplitude of the unipolar output signal is sampled is not less than about 6 KHz.
 4. A method for generating an audible warning of an equipment malfunction comprising the steps of: a. generating a continuously variable analog electrical signal within a frequency range from about 20 Hz. to about 20 KHz.; b. filtering the generated electrical signal to substantially eliminate frequency components below about 200 Hz. and above about 3 KHz.; c. limiting the amplitude of the filtered signal to a predetermined value; d. periodically sampling the amplitude of the amplitude limited signal at a fixed sampling rate; e. converting each of the amplitude samples to a corresponding signal whereby said analog electrical signal is converted to a serial train of fixed-bit-length digital condes; f. serially storing said fixed-bit-length digital codes in a non-volatile memory circuit; g. generating an electrical enabling signal in response to an equipment malfunction; h. generating a train of sequential memory addressing pulses in response to said enabling signal; i. reading out the stored content of said memory circuit in a non-repetitive serial sequence to produce therefrom a sequential series of digital data signals in response to the application of said memory addressing pulse train thereto; j. converting each of the digital data signals to a corresponding amplitude sample; k. integrating the amplitude samples to provide an analog signal; and, l. transducing the analog signal into an audible warning.
 5. The method of claim 4 including the steps of: converting the amplitude limited signal to a unipolar output signal prior to sampling the amplitude thereof.
 6. The method of claim 4 wherein the frequency at which the amplitude of the amplitude-limited signal is sampled is not less than about 6 KHz.
 7. An aircraft voice warning system comprising: a plurality of sensors each adapted to sense a condition of the aircraft; means for storing a digital data signal representative of an audio message for each of said plurality of sensors; a source of digital pulses having a predetermined pulse repetition rate; a first binary counter for converting the number of pulses applied thereto to a binary output signal; means responsive to one of said sensors for passing pulses from said source to said first binary counter; a first decoder for converting the binary output signals from said first binary counter to a line read-out signal; a second counter responsive to pulses from said first binary Counter for converting the number of pulses applied thereto to a binary output signal; a second decoder for converting the binary output signals from said second counter to a row read-out signal; a permanent solid-state read-only memory circuit for providing digital data signals in response to said line and row read-out signals, said digital data signals each being relating to the instantaneous amplitude of an audio frequency signal; second converting means for converting said digital data signals to amplitude samples; means for integrating said amplitude samples to provide an analog signal; and means for transducing said analog signal into a voice warning.
 8. The system of claim 7 including means for generating a signal for disabling said first converting means; and means for recycling said first converting means after a predetermined time delay in the absence of a signal from said disabling means.
 9. Apparatus for permanently storing signals representative of compressional wave energy comprising: means for generating an analog electrical signal representative of compressional wave energy within a frequency range from about 20 Hz. to about 20 KHz.; biasing means for changing the generated analog signal to a unipolar output signal; means limiting the amplitude of the generated analog signal to a predetermined value prior to the changing of said analog signal to a unipolar output signal; means for periodically sampling the amplitude of frequency components of said unipolar output signal within a frequency range substantially less than the frequency range of the generated signal; converting means synchronized with said sampling means for generating a series of pulses related in number to the sampled amplitude, and for converting the number of generated pulses into binary form, said converting means including means for generating a comparing signal varying in amplitude as a function of time; means for comparing the amplitude of said sample with the amplitude of said comparing signal; a source of pulses having a predetermined pulse repetition rate; and, a binary counter for receiving pulses from said source during a period of time initiated by a pulse from said source and terminated by the output from said comparing means; and, means for permanently storing the digital signals.
 10. Apparatus for generating an audible warning of an equipment malfunction, comprising: a source of continuously variable analog electrical signals representative of an audio message; means for biasing said analog signals to result in a corresponding unipolar output signal; means for periodically sampling the instantaneous amplitude of said unipolar output signal at a fixed sampling rate within a frequency range substantially less than the frequency range of said analog signal; a non-volatile digital memory for serially storing a plurality of fixed-bit length digital codes; means connected to the output of said sampling means and to the input of said digital memory for converting each of the amplitude samples from said sampling means to a corresponding fixed-bit pulse code modulation signal for storage in said memory as serially-arranged fixed-bit-length digital codes; means for producing an electrical enabling signal in response to an equipment malfunction; means for generating a train of sequential memory addressing pulses in response to said enabling signal; means connecting said memory addressing pulse generating means to said digital memory whereby the content of said digital memory is read out in a non-repetitive serial sequence to produce, at the output of said memory, a sequential series of digital data signals in response to each application of said memory addressing pulse train thereto; means for converting each of the digital data signals from the output of said memory to a corresponding amplitude sample; means for integrating the amplitudE samples from said digital signal converting means to provide an analog output signal; and means for transducing said analog output signal into an audible warning.
 11. Apparatus for generating an audible warning of an equipment malfunction, comprising: means for generating a continuously variable analog electrical signal within a frequency range from about 20 Hz. to about 20 KHz.; means for filtering said analog electrical signal to substantially eliminate frequency components therefrom below about 200 Hz. and above about 3 KHz.; a limiter for constraining the amplitude of the filtered signal to a predetermined value; sampling means for periodically sampling the amplitude of the amplitude-limited signal at a fixed sampling rate; means connected to the output of said sampling means for converting each of the amplitude samples to a corresponding signal whereby said analog electrical signal is converted to a serial train of fixed-bit-length digital codes at the output thereof; a non-volatile digital memory connected to the output of said converting means for serially storing said train of fixed-bit-length digital codes; means for producing an electrical enabling signal in response to an equipment malfunction; means for generating a train of sequential memory addressing pulses in response to said enabling signal; means connecting said memory addressing pulse generating means to said digital memory whereby the content of said digital memory is read out in a non-repetitive serial sequence to produce, at the output of said memory, a sequential series of digital data signals in response to each application of said memory addressing pulse train thereto; means for converting each of the digital data signals from the output of said memory to a corresponding amplitude sample; means for integrating the amplitude samples from said digital signal converting means to provide an analog output signal; and means for transducing said analog output signal into an audible warning.
 12. Apparatus for permanently storing signals representative of compressional wave energy comprising: means for generating an analog electrical signal representative of compressional wave energy within a frequency range from about 20 Hz. to about 20 KHz.; biasing means for changing the generated analog signal to a unipolar output signal; means for limiting the amplitude of the generated analog signal to a predetermined value prior to the changing of said analog signal to a unipolar output signal; means for periodically sampling the amplitude of frequency components of said unipolar output signal within a frequency range substantially less than the frequency range of the generate signal; converting means synchronized with said sampling means generating a series of pulses related in number to the sampled amplitude, and for converting the number of generated pulses into binary form; and, a solid-state non-destructive read-only memory for permanently storing the digital signals. 